The present invention is directed to the application of pressurized liquid to a semiconductor wafer or similar workpiece, and more particularly concerns the removal therefrom of vapor introduced during regulation of the liquid flow.
During the manufacture of integrated circuits on a semiconductor wafer, a photoresist applied to the top surface of the wafer. The wafer is placed in a chuck of a stepper tool for exposing the photoresist in a pattern which defines the devices and interconnection of the circuits to be formed on the wafer. To avoid contamination of the chuck, the photoresist must be kept off the back side of the wafer, and preferably also away from a thin bead around the periphery of the front side.
Conventionally, a very small amount of solvent liquid is dispensed at low pressure for a short time onto carefully determined areas of the wafer while the photoresist coating is being applied, so as to dissolve any photoresist in those areas. However, regulating the flow of this pressurized solvent introduces vapor bubbles into the liquid. A conventional needle valve, for example, regulates the flow very well, but it also generates a stream of tiny bubbles in the highly volatile solvent. These bubbles cause the dispensed solvent to splash into undesired wafer areas, producing pinholes in the photoresist, which ultimately result in defects in the integrated circuits on the wafer. Turning the flow on and off during the process also tends to introduce bubbles, and renders conventional bubble-extraction methods ineffective.
Liquids used for such solvents are highly volatile and flammable, thus compounding the problems in handling them.